Not available these days as there's only demand in one direction.
What if you were to rent a car in Buffalo (with a scheduled return in Buffalo) and attempt to drop it off in Toronto?
I found this on the Hertz web site:
"A Return Change Fee of $12.99 will be applied if you return the vehicle to a different location from that which was scheduled, or if you return more than 12 hours after the date and time previously scheduled, and you failed to notify Hertz of such a change more than 24 hours prior to your scheduled return time by calling Hertz at 1-800-654-4174."
This fee will be applied in addition to any change in rental rate that occurs as a result of extending your rental."